Titanium dioxide, also known astitanium(IV) oxide ortitania/taɪˈteɪniə/, is theinorganic compound derived fromtitanium with the chemical formulaTiO 2. When used as apigment, it is calledtitanium white,Pigment White 6 (PW6), orCI 77891.[3] It is a white solid that is insoluble in water, although mineral forms can appear black. As a pigment, it has a wide range of applications, includingpaint,sunscreen, andfood coloring. When used as a food coloring, it hasE number E171. World production in 2014 exceeded 9 million tonnes.[4][5][6] It has been estimated that titanium dioxide is used in two-thirds of all pigments, and pigments based on the oxide have been valued at a price of $13.2 billion.[7]
Structure ofanatase. Together with rutile and brookite, one of the three majorpolymorphs of TiO2.
In all three of its main dioxides,titanium exhibitsoctahedral geometry, being bonded to six oxide anions. The oxides in turn are bonded to three Ti centers. The overall crystal structures ofrutile andanatase are tetragonal in symmetry whereasbrookite is orthorhombic. The oxygen substructures are all slight distortions ofclose packing: in rutile, the oxide anions are arranged in distorted hexagonal close-packing, whereas they are close to cubic close-packing in anatase and to "double hexagonal close-packing" for brookite. Therutile structure is widespread for other metal dioxides and difluorides, e.g. RuO2 and ZnF2.
Molten titanium dioxide has a local structure in which each Ti is coordinated to, on average, about 5 oxygen atoms.[8] This is distinct from the crystalline forms in which Ti coordinates to 6 oxygen atoms.
Synthetic TiO2 is mainly produced from the mineralilmenite.Rutile, andanatase, naturally occurring TiO2, occur widely also, e.g. rutile as a 'heavy mineral' in beach sand.Leucoxene, fine-grained anatase formed by natural alteration of ilmenite, is yet another ore.Star sapphires andrubies get theirasterism from oriented inclusions of rutile needles.[9]
Titanium dioxide occurs in nature as the mineralsrutile andanatase. Additionally two high-pressure forms are known minerals: amonoclinicbaddeleyite-like form known asakaogiite, and the other has a slight monoclinic distortion of theorthorhombicα-PbO2 structure and is known as riesite. Both of which can be found at theRies crater inBavaria.[10][11][12] It is mainly sourced fromilmenite, which is the most widespread titanium dioxide-bearing ore around the world. Rutile is the next most abundant and contains around 98% titanium dioxide in the ore. The metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase upon heating above temperatures in the range 600–800 °C (1,110–1,470 °F).[13]
Titanium dioxide has twelve known polymorphs – in addition to rutile, anatase, brookite, akaogiite and riesite, three metastable phases can be produced synthetically (monoclinic,tetragonal, and orthorhombic ramsdellite-like), and four high-pressure forms (α-PbO2-like,cotunnite-like, orthorhombic OI, and cubic phases) also exist:
Thecotunnite-type phase was claimed to be the hardest known oxide with theVickers hardness of 38 GPa and thebulk modulus of 431 GPa (i.e. close to diamond's value of 446 GPa) at atmospheric pressure.[21] However, later studies came to different conclusions with much lower values for both the hardness (7–20 GPa, which makes it softer than common oxides like corundum Al2O3 and rutile TiO2)[22] and bulk modulus (~300 GPa).[23][24]
Titanium dioxide (B) is found as amineral in magmatic rocks and hydrothermal veins, as well as weathering rims onperovskite. TiO2 also formslamellae in other minerals.[25]
The production method depends on the feedstock. In addition to ores, other feedstocks include upgradedslag. Both the chloride process and the sulfate process (both described below) produce titanium dioxide pigment in the rutile crystal form, but the sulfate process can be adjusted to produce theanatase form. Anatase, being softer, is used in fiber and paper applications. The sulfate process is run as abatch process; the chloride process is run as acontinuous process.[30]
Inchloride process, the ore is treated with chlorine and carbon to givetitanium tetrachloride, a volatile liquid that is further purified by distillation. The TiCl4 is treated withoxygen to regenerate chlorine and produce the titanium dioxide.
In the sulfate process, ilmenite is treated withsulfuric acid to extractiron(II) sulfate pentahydrate. This process requires concentrated ilmenite (45–60% TiO2) or pretreated feedstocks as a suitable source of titanium.[31] The resulting synthetic rutile is further processed according to the specifications of the end user, i.e. pigment grade or otherwise.[32]
TheBecher process is another method for the production of synthetic rutile from ilmenite. It first oxidizes the ilmenite as a means to separate the iron component.
For specialty applications, TiO2 films are prepared by various specialized chemistries.[34] Sol-gel routes involve the hydrolysis of titaniumalkoxides such astitanium ethoxide:
Ti(OEt)4 + 2 H2O → TiO2 + 4 EtOH
A related approach that also relies on molecular precursors involveschemical vapor deposition. In this method, the alkoxide is volatilized and then decomposed on contact with a hot surface:
First mass-produced in 1916,[35] titanium dioxide is the most widely used white pigment because of its brightness and very highrefractive index, in which it is surpassed only by a few other materials (seelist of indices of refraction). Titanium dioxide crystal size is ideally around 220 nm (measured by electron microscope) to optimize the maximum reflection of visible light. However,abnormal grain growth is often observed in titanium dioxide, particularly in its rutile phase.[36] The occurrence of abnormal grain growth brings about a deviation of a small number of crystallites from the mean crystal size and modifies the physical behaviour of TiO2. The optical properties of the finished pigment are highly sensitive to purity. As little as a few parts per million (ppm) of certain metals (Cr, V, Cu, Fe, Nb) can disturb the crystal lattice so much that the effect can be detected in quality control.[37][full citation needed][38] Approximately 4.6 million tons of pigmentary TiO2 are used annually worldwide, and this number is expected to increase as use continues to rise.[39]
TiO2 is also an effectiveopacifier in powder form, where it is employed as a pigment to provide whiteness andopacity to products such as paints, coatings, plastics, papers, inks, foods,supplements, medicines (i.e. pills and tablets), and most toothpastes; in 2019 it was present in two-thirds of toothpastes on the French market.[40] In paint, it is often referred to offhandedly as "brilliant white", "the perfect white", "the whitest white", or other similar terms. Opacity is improved by optimal sizing of the titanium dioxide particles.
Often used as color in food,[41] it is commonly found in ice creams, chocolates, all types of candy, creamers, desserts, marshmallows, chewing gum, pastries, spreads, dressings, cakes, some cheeses, and many other foods.[42] It is permitted in many countries, but was banned for use in food by the European Union in 2022. While permitted in the United States,Mars removed it from theirSkittles confectionery in 2025, although a class-action lawsuit against the use of titanium dioxide in Skittles had been dismissed in 2022.[43]
When deposited as athin film, its refractive index and colour make it an excellent reflective optical coating fordielectric mirrors; it is also used in generating decorative thin films such as found in "mystic fire topaz".[citation needed]
Some grades of modified titanium based pigments as used in sparkly paints, plastics, finishes and cosmetics – these are man-made pigments whose particles have two or more layers of various oxides – often titanium dioxide,iron oxide oralumina – in order to have glittering,iridescent and orpearlescent effects similar to crushedmica orguanine-based products. In addition to these effects a limited colour change is possible in certain formulations depending on how and at which angle the finished product is illuminated and the thickness of the oxide layer in the pigment particle; one or more colours appear by reflection while the other tones appear due to interference of the transparent titanium dioxide layers.[44] In some products, the layer of titanium dioxide is grown in conjunction with iron oxide by calcination of titanium salts (sulfates, chlorates) around 800 °C[45] One example of a pearlescent pigment is Iriodin, based on mica coated with titanium dioxide or iron (III) oxide.[46]
The iridescent effect in these titanium oxide particles is unlike the opaque effect obtained with usual ground titanium oxide pigment obtained by mining, in which case only a certain diameter of the particle is considered and the effect is due only to scattering.
In cosmetic and skin care products, titanium dioxide is used as a pigment, sunscreen and a thickener. As a sunscreen, ultrafine TiO2 is used, which is notable in that combined withultrafine zinc oxide, it is considered to be an effective sunscreen that lowers the incidence ofsun burns and minimizes the prematurephotoaging,photocarcinogenesis andimmunosuppression associated with long term excess sun exposure.[47] Sometimes these UV blockers are combined with iron oxide pigments in sunscreen to increase visible light protection.[48]
Nanosized titanium dioxide is found in the majority of physical sunscreens because of its strong UV light absorbing capabilities and its resistance to discolouration underultraviolet light. This advantage enhances its stability and ability to protect the skin from ultraviolet light. Nano-scaled (particle size of 20–40 nm)[50] titanium dioxide particles are primarily used in sunscreen lotion because they scatter visible light much less than titanium dioxide pigments, and can give UV protection.[39] Sunscreens designed for infants or people withsensitive skin are often based on titanium dioxide and/orzinc oxide, as these mineral UV blockers are believed to cause less skin irritation than other UV absorbing chemicals. Nano-TiO2, which blocks both UV-A and UV-B radiation, is used in sunscreens and other cosmetic products.
The EU Scientific Committee on Consumer Safety considered nano sized titanium dioxide to be safe for skin applications, in concentrations of up to 25 percent based on animal testing.[51] The risk assessment of different titanium dioxide nanomaterials in sunscreen is currently evolving since nano-sized TiO2 is different from the well-known micronized form.[52] The rutile form is generally used in cosmetic and sunscreen products due to it not possessing any observed ability to damage the skin under normal conditions[53] and having a higherUV absorption.[54] In 2016 Scientific Committee on Consumer Safety (SCCS) tests concluded that the use of nano titanium dioxide (95–100% rutile, ≦5% anatase) as a UV filter can be considered to not pose any risk of adverse effects in humans post-application on healthy skin,[55] except in the case the application method would lead to substantial risk of inhalation (ie; powder or spray formulations). This safety opinion applied to nano TiO2 in concentrations of up to 25%.[56]
Initial studies indicated that nano-TiO2 particles could penetrate the skin, causing concern over its use. These studies were later refuted, when it was discovered that the testing methodology couldn't differentiate between penetrated particles and particles simply trapped in hair follicles and that having a diseased or physically damaged dermis could be the true cause of insufficient barrier protection.[52]
SCCS research found that when nanoparticles had certain photostable coatings (e.g.,alumina,silica, cetyl phosphate,triethoxycaprylylsilane,manganese dioxide), the photocatalytic activity was attenuated and no notable skin penetration was observed; the sunscreen in this research was applied at amounts of 10 mg/cm2 for exposure periods of 24 hours.[56] Coating TiO2 with alumina, silica,zircon or variouspolymers can minimizeavobenzone degradation[57] and enhance UV absorption by adding an additional light diffraction mechanism.[54]
TiO 2 is used extensively in plastics and other applications as a white pigment or an opacifier and for its UV resistant properties where the powder disperses light – unlike organic UV absorbers – and reduces UV damage, due mostly to the particle's high refractive index.[58]
It is used as atattoo pigment and instyptic pencils. Titanium dioxide is produced in varying particle sizes which are both oil and water dispersible, and in certain grades for the cosmetic industry. It is also a common ingredient in toothpaste.
The exterior of theSaturn V rocket was painted with titanium dioxide; this later allowed astronomers to determine thatJ002E3 was likely theS-IVB stage fromApollo 12 and not anasteroid.[59]
Relevant patent families describing titanium dioxide production from ilmenite, 2002–2021.Academic and public institutions having significant patent activity in titanium dioxide production, 2022.
Between 2002 and 2022, there were 459patent families that describe the production of titanium dioxide fromilmenite. The majority of these patents describe pre-treatment processes, such as using smelting and magnetic separation to increase titanium concentration in low-grade ores, leading to titanium concentrates or slags. Other patents describe processes to obtain titanium dioxide, either by a direct hydrometallurgical process or through the main industrial production processes, thesulfate process and thechloride process.[62] The sulfate process represents 40% of the world's titanium dioxide production and is protected in 23% of patent families. The chloride process is only mentioned in 8% of patent families, although it provides 60% of the worldwide industrial production of titanium dioxide.[62]
Key contributors to patents on the production of titanium dioxide are companies from China, Australia and the United States, reflecting the major contribution of these countries to industrial production. Chinese companiesPangang andLomon Billions Groups hold major patent portfolios.[62]
Nanosized titanium dioxide, particularly in the anatase form, exhibitsphotocatalytic activity under ultraviolet (UV) irradiation. This photoactivity is reportedly most pronounced at the {001} planes of anatase,[63][64] although the {101} planes are thermodynamically more stable and thus more prominent in most synthesised and natural anatase,[65] as evident by the often observed tetragonal dipyramidalgrowth habit. Interfaces between rutile and anatase are further considered to improve photocatalytic activity by facilitating charge carrier separation and as a result, biphasic titanium dioxide is often considered to possess enhanced functionality as a photocatalyst.[66] It has been reported that titanium dioxide, when doped with nitrogen ions or doped with metal oxide like tungsten trioxide, exhibits excitation also under visible light.[67] The strongoxidative potential of thepositive holes oxidizes water to createhydroxyl radicals. It can also oxidize oxygen or organic materials directly. Hence, in addition to its use as a pigment, titanium dioxide can be added to paints, cements, windows, tiles, or other products for its sterilizing, deodorizing, and anti-fouling properties, and is used as ahydrolysiscatalyst. It is also used indye-sensitized solar cells, which are a type of chemical solar cell (also known as a Graetzel cell).
The photocatalytic properties of nanosized titanium dioxide were discovered byAkira Fujishima in 1967[68] and published in 1972.[69] The process on the surface of the titanium dioxide was called theHonda-Fujishima effect [ja].[68] Inthin film andnanoparticle form, titanium dioxide has the potential for use in energy production: As a photocatalyst, it can break water into hydrogen and oxygen. With the hydrogen collected, it could be used as a fuel. The efficiency of this process can be greatly improved by doping the oxide with carbon.[70] Further efficiency and durability has been obtained by introducing disorder to the lattice structure of the surface layer of titanium dioxide nanocrystals, permitting infrared absorption.[71] Visible-light-active nanosized anatase and rutile has been developed for photocatalytic applications.[72][73]
In 1995 Fujishima and his group discovered thesuperhydrophilicity phenomenon for titanium dioxide coated glass exposed to sun light.[68] This resulted in the development ofself-cleaning glass andanti-fogging coatings.
Nanosized TiO2 incorporated into outdoor building materials, such as paving stones innoxer blocks[74] or paints, could reduce concentrations of airborne pollutants such asvolatile organic compounds andnitrogen oxides.[75] A TiO2-containing cement has been produced.[76]
Using TiO2 as a photocatalyst, attempts have been made to mineralize pollutants (to convert into CO2 and H2O) in waste water.[77][78][79] The photocatalytic destruction of organic matter could also be exploited in coatings with antimicrobial applications.[80]
Although nanosized anatase TiO2 does not absorb visible light, it does strongly absorbultraviolet (UV) radiation (hv), leading to the formation of hydroxyl radicals.[81] This occurs when photo-induced valence bond holes (h+vb) are trapped at the surface of TiO2 leading to the formation of trapped holes (h+tr) that cannot oxidize water.[82]
Note: Wavelength (λ)= 387 nm[82] This reaction has been found to mineralize and decompose undesirable compounds in the environment, specifically the air and in wastewater.[82]
Synthetic single crystals of TiO2, c. 2–3 mm in size, cut from a larger plate
Nanotubes of titanium dioxide (TiO2-Nt) obtained by electrochemical synthesis. The SEM image shows an array of vertical self-ordered TiO2-Nt with closed bottom ends of tubes.
Titanium dioxide is insoluble in water, organic solvents, and inorganic acids. It is slightly soluble inalkali, soluble in saturated potassium bicarbonate, and can be completely dissolved in strongsulfuric acid andhydrofluoric acid after boiling for a long time.[85]
Widely occurring minerals and even gemstones are composed of TiO2. All natural titanium, comprising more than 0.5% of the Earth's crust, exists as oxides.[86]
As of 2024, titanium dioxide is considered safe by the USFDA as a color ingredient for oral human consumption as long as it is 1% or less of the total food composition.[87] A 2021 ban by the EUEFSA has been criticized as based on errors regarding the safety of titanium dioxide (E171) particles as a food additive,[88] and according to a 2022 review, existing evidence does not support a direct DNA damaging mechanism for titanium dioxide.[89]
TiO2 whitener in food was banned in France from 2020, due to uncertainty about safe quantities for human consumption.[90]
In 2021, theEuropean Food Safety Authority (EFSA) ruled that as a consequence of new understandings ofnanoparticles, titanium dioxide could "no longer be considered safe as a food additive", and the EU health commissioner announced plans to ban its use across the EU, with discussions beginning in June 2021. EFSA concluded thatgenotoxicity—which could lead tocarcinogenic effects—could not be ruled out, and that a "safe level for daily intake of the food additive could not be established".[91] In 2022, the UK Food Standards Agency and Food Standards Scotland announced their disagreement with the EFSA ruling, and did not follow the EU in banning titanium dioxide as a food additive.[92] Health Canada similarly reviewed the available evidence in 2022 and decided not to change their position on titanium dioxide as a food additive.[93]
The European Union removed the authorization to use titanium dioxide (E 171) in foods, effective 7 February 2022, with a six months grace period.[94]
As of May 2023, following the European Union 2022 ban, the U.S. statesCalifornia andNew York were considering banning the use of titanium dioxide in foods.[95]
As of 2024, theFood and Drug Administration (FDA) in the United States permits titanium dioxide as a food additive.[87] It may be used to increase whiteness and opacity in dairy products (some cheeses, ice cream, and yogurt), candies, frostings, fillings, and many other foods. The FDA regulates the labeling of products containing titanium dioxide, allowing the product's ingredients list to identify titanium dioxide either as "color added" or "artificial colors" or "titanium dioxide;" it does not require that titanium dioxide be explicitly named.[87] In 2023, theConsumer Healthcare Products Association, a manufacturer's trade group, defended the substance as safe at certain limits while allowing that additional studies could provide further insight, saying an immediate ban would be a "knee-jerk" reaction.[96]
Size distribution analyses showed that batches of food-grade TiO₂, which is produced with a target particle size in the 200–300nm range for optimal pigmentation qualities, include a nanoparticle-sized fraction as inevitable byproduct of the manufacturing processes.[98]
Although no evidence points to acute toxicity, recurring concerns have been expressed about nanophase forms of these materials. Studies of workers with high exposure to TiO2 particles indicate that even at high exposure there is no adverse effect to human health.[86]
Titanium dioxide (TiO₂) is mostly introduced into the environment asnanoparticles via wastewater treatment plants.[102] Cosmetic pigments including titanium dioxide enter the wastewater when the product is washed off into sinks after cosmetic use. Once in the sewage treatment plants, pigments separate into sewage sludge which can then be released into the soil when injected into the soil or distributed on its surface. 99% of these nanoparticles wind up on land rather than in aquatic environments due to their retention in sewage sludge.[102] In the environment, titanium dioxide nanoparticles have low to negligible solubility and have been shown to be stable once particle aggregates are formed in soil and water surroundings.[102] In the process of dissolution, water-soluble ions typically dissociate from the nanoparticle into solution when thermodynamically unstable. TiO2 dissolution increases when there are higher levels of dissolved organic matter and clay in the soil. However, aggregation is promoted by pH at the isoelectric point of TiO2 (pH= 5.8) which renders it neutral and solution ion concentrations above 4.5 mM.[103][104]
^Marchand R., Brohan L., Tournoux M. (1980). "A new form of titanium dioxide and the potassium octatitanate K2Ti8O17".Materials Research Bulletin.15 (8):1129–1133.doi:10.1016/0025-5408(80)90076-8.
^Akimoto J, Gotoh Y, Oosawa Y, Nonose N, Kumagai T, Aoki K, Takei H (1994). "Topotactic Oxidation of Ramsdellite-Type Li0.5TiO2, a New Polymorph of Titanium Dioxide: TiO2(R)".Journal of Solid State Chemistry.113 (1):27–36.Bibcode:1994JSSCh.113...27A.doi:10.1006/jssc.1994.1337.
^Dubrovinskaia N. A., Dubrovinsky L. S., Ahuja R., Prokopenko V. B., Dmitriev V., Weber H.-P., Osorio-Guillen J. M., Johansson B. (2001). "Experimental and Theoretical Identification of a New High-Pressure TiO2 Polymorph".Phys. Rev. Lett.87 (27 Pt 1) 275501.Bibcode:2001PhRvL..87A5501D.doi:10.1103/PhysRevLett.87.275501.PMID11800890.
^Nishio-Hamane D., Shimizu A., Nakahira R., Niwa K., Sano-Furukawa A., Okada T., Yagi T., Kikegawa T. (2010). "The stability and equation of state for the cotunnite phase of TiO2 up to 70 GPa".Phys. Chem. Miner.37 (3):129–136.Bibcode:2010PCM....37..129N.doi:10.1007/s00269-009-0316-0.S2CID95463163.
^Anderson B (1999).Kemira pigments quality titanium dioxide. Savannah, Georgia. p. 39.{{cite book}}: CS1 maint: location missing publisher (link)
^Karvinen SM (2003) [Dec 21, 2002]. "The effects of trace element doping on the optical properties and photocatalytic activity of nanostructured titanium dioxide".Ind. Eng. Chem. Res.42 (5). American Chemical Society:1035–1043.doi:10.1021/ie020358z.
^abWinkler J (2003).Titanium Dioxide. Hannover, Germany: Vincentz Network. p. 5.ISBN978-3-87870-148-4.
^Li Jianming and Dongsheng Xu (2010). "tetragonal faceted-nanorods of anatase TiO2 single crystals with a large percentage of active {100} facets".Chemical Communications.46 (13):2301–3.doi:10.1039/b923755k.PMID20234939.
^Kurtoglu M. E., Longenbach T., Gogotsi Y. (2011). "Preventing Sodium Poisoning of Photocatalytic TiO2 Films on Glass by Metal Doping".International Journal of Applied Glass Science.2 (2):108–116.doi:10.1111/j.2041-1294.2011.00040.x.
^"Carbon-doped titanium dioxide is an effective photocatalyst".Advanced Ceramics Report. 1 December 2003. Archived fromthe original on 4 February 2007.This carbon-doped titanium dioxide is highly efficient; under artificial visible light, it breaks down chlorophenol five times more efficiently than the nitrogen-doped version.
^Winkler J (2003).Titanium Dioxide. Hannover: Vincentz Network. pp. 115–116.ISBN978-3-87870-148-4.
^Konstantinou IK, Albanis TA (2004). "TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: Kinetic and mechanistic investigations".Applied Catalysis B: Environmental.49 (1):1–14.Bibcode:2004AppCB..49....1K.doi:10.1016/j.apcatb.2003.11.010.
^Hanaor DA, Sorrell CC (2014). "Sand Supported Mixed-Phase TiO2 Photocatalysts for Water Decontamination Applications".Advanced Engineering Materials.16 (2):248–254.arXiv:1404.2652.doi:10.1002/adem.201300259.S2CID118571942.
^abcHirakawa T, Nosaka Y (23 January 2002). "Properties of O2•-and OH• formed in TiO2 aqueous suspensions by photocatalytic reaction and the influence of H2O2 and some ions".Langmuir.18 (8):3247–3254.doi:10.1021/la015685a.
^Mogilevsky G, Chen Q, Kleinhammes A, Wu Y (2008). "The structure of multilayered titania nanotubes based on delaminated anatase".Chemical Physics Letters.460 (4–6):517–520.Bibcode:2008CPL...460..517M.doi:10.1016/j.cplett.2008.06.063.
^Preočanin T, Kallay N (2006). "Point of Zero Charge and Surface Charge Density of TiO2 in Aqueous Electrolyte Solution as Obtained by Potentiometric Mass Titration".Croatica Chemica Acta.79 (1):95–106.ISSN0011-1643.
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![SEM (top) and TEM (bottom) images of chiral TiO2 nanofibers[84]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aChiral_TiO2_nanofibers_2.jpg)
